G320 losing position

[rbcmetalwork]

I have a 3-axis retrofit knee mill with G320s. The X and Y axes operate fine. They are accurate and repeatable. The Z axis is the problem. It homes okay but movements are not accurate nor repeatable. Troubleshooting (swapping drives, wiring, step/direction signal) narrowed the problem down to the G320. Gecko told me that indeed the drive had a problem. They sent me a new one. The newly installed G320 is better (positioning/repeatability error is less than before) but the problem persists. Please help.

Randy
Honolulu, Hawaii

[mc-motorsports]

Maybe a problem with the ballscrew?

What encodor are you using? Actual brand and line count?

[rbcmetalwork]

The servo motor/encoder is by Baldor. 1000 cpr. The ballscrews are 5 tpi.

In my troubleshooting, I swapped motors, X for Z, and the X-axis worked fine. Conclusion: Z-axis motor is okay.

I also used the Z-axis step/direction to move the X-axis accurately and repeatably. Conclusion: the breakout board signal is okay.

I was able to get the Z-axis working accurately and repeatably by using the X-axis G320. Conclusion: the Z-axis G320 was the problem.

Have I made an error somewhere?

[mc-motorsports]

Are all 3 servo's the same manufacture? And all encodors are the same manufacture?

The Z axis driver is not repeatable, but if you use another existing known good driver, everything is ok... But you already replaced the Z axis driver and have the same problems with a new drive? Wow. If you had a faulty drive, I would say it falls under the "stuff happens" catagory. If Gecko sent you another drive and that one is bad too??? I would think there is something causing the drive to fail. Gecko normally has excellent quality, but like I said, "stuff happens" and it's not impossible that a bad drive slipped out the door. 2 in a row???

I had a similar problem. All 3 drives failed, it was because of mis-matched encodors. The encoders were drawing too much amperage (renco?) and caused the drives to fail and or fault. I sent them back to Gecko for testing, 1 was beyond repair, 1 was repairable and 1 was fine. All 3 servo's were the same, all 3 encoders were the same. Gecko called me, through conversation, diagnosed the problem, sent me 1 new driver, 1 repaired driver and returned the good driver. They also told me were to get the proper encoders to work with the Gecko Drives, I think US Encoder, everything has worked great since with absolutly no issue and I can't say enough good things about Gecko and thier customer service. The engineer over there really knows his stuff!

Next question, are you dealing directly with Gecko or with a distributor/company who supplies retrofit components?

[rbcmetalwork]

All three motor/encoders are of the same manufacturer and model.

The (3) G320s were purchased directly from Geckodrive. They told me that their technicians found that the G320 was inconsistent and that they were stumped as to why.

[rbcmetalwork]

After an educational phone conversation with Mariss, the culprit seems to be the encoders which are drawing too much current for the G320s.

[mc-motorsports]

I'm sure Mariss told you where to get the proper encodors and such. I'm sure once you get everything up and running, you'll be very happy. Thanks to Mariss, I got the right encodors and have been running with absolutley no problems for 2 years.
Good stuff!

[mc-motorsports]

BTW, my problem was the guy who sold me the complete package of a control unit using Gecko drives, 3 servo's and the 3 encodors that were installed drew too much current. The system failed immediatly. I called the guy who sold me the stuff, he was no help. Called Gecko, they got me fixed right up! Marriss told me everything that I needed to do to clean up the other guys mess. I called the guy who sold me the complete system and he avoided me like the plauge... Never did make right for his mistakes which cost me more money, I think he went out of business, wonder why...

[rbcmetalwork]

I purchased and installed 3 new U.S. Digital single ended encoders. They passed the encoder test fine. However, the motor won't lock. Same problem on all three axes. More phone calls to Mariss. Seems like the encoder signal is getting disturbed when the motors are connected. Keep in mind that these same G320s worked fine with the old encoders drawing 160mA. I'm going to change to differential encoders and see if that works.

[rbcmetalwork]

I removed the single ended encoder and installed the differential encoder on the X-axis motor. The motor now locks and rotates fine. Y and Z axes next.

[mc-motorsports]

That's new to me, haven't heard that one before. What encoders are you using now? Did you figure out what was wrong with the old ones?

[rbcmetalwork]

I coupled the X-axis motor to the ball screw and did some accuracy tests. No joy. I'm still losing position. Not accurate nor repeatable. I use the glass scales from my DRO as a reference for positioning.

My next plan is to purchase and try the twisted pair cables and differential receivers. That should hopefully rule out any noise issues with the encoders. My X-axis cable is about 6-feet long which just so happens to be the length at which they don't recommend a single ended encoder.

The differential encoders on there now are from U.S. Digital, part number H15-500-N-D. The original Sumtak encoders worked (on the X and Y axes but not on Z), although the 1000 CPR was a little high and they draw 160mA.